The present invention relates to a folding machine, particularly for folding signatures of a printed sheet.
Here and hereinafter, the term "sheet material" is intended to mean either a single sheet or a signature produced by folding the same.
A standard practice in the printing industry is to print a number of pages of a given text on one sheet, which is then fed on to a folding machine in which the sheet is fed through one or more folding stations to form a respective signature.
At each folding station, the sheet is folded in half as often as required for forming the signature, each page of which normally corresponds with a page of the printed text.
On commonly used folding machines, for folding the sheet as described above, each folding station features at least one folding unit defined by two counter-rotating rollers between which an intermediate portion of the sheet is fed by means of units usually comprising a conveyor for feeding the sheet transversely in relation to the rollers of the respective folding unit, and a knife device facing, parallel to, and moving back and forth in relation to the folding rollers.
The knife device provides for engaging the intermediate portion of the sheet transversely in relation to the traveling direction, and for feeding it between the two counter-rotating rollers by which the sheet is folded in half and either fed to the output or to a further folding station.
On known folding machines of the aforementioned type, the folding and feed units of all the folding stations are generally powered, in time with one another, by a single motor, which, while on the one hand providing for substantial saving in terms of machinery cost, and for simplifying timing of the various folding stations, on the other, practically eliminates any and all flexibility of the machinery in terms of output rate. This, in fact, is limited to the maximum rate compatible with the mechanical resistance of the most highly stressed components on the machine, and allows of substantially no variation for different sheet formats, i.e. for increasing the output rate in inverse proportion to the sheet format for a given stress on the machine components.